Oil and gas offshore drilling operations require the use of a riser or riser string as it is also known. The riser consists of a string of pipe that extends from a floating drilling platform down to the sea floor. The riser is comprised of riser components that are attached end-to-end by means of flanged or custom connections. Drilling mud, cuttings and hydrocarbon products from the borehole in the seafloor are returned to the drilling platform through the riser. The top of the riser is attached to the drilling platform while its lower end is secured to the wellhead on the seafloor. Immediately below the drilling platform, the riser has a slip joint, or tension joint as it is also known, that is configured to telescope to compensate for the heave and swell that the floating drilling platform experiences in the sea.
It is conventional to use a subsurface blowout preventer (a “BOP”) placed between the wellhead and the riser to provide protection against the sudden release of gas, which can arise if the drilling operations encounter pressurized formations. To promote safety and control, a surface BOP is also frequently placed at the top of the riser proximate to the drilling platform.
It is also conventional to use a surface rotating flow control device (a “RFCD”) at the level of the drilling platform in conjunction with the surface BOP. The surface RFCD serves multiple purposes including the provision of a pressure seal around drill pipe that is being moved in and out of the riser and the wellbore while allowing rotation of same. Conventional diverters are also placed at the head of the riser above the slip joint to divert wellbore returns to the surface separation and storage equipment.
While the use of a surface BOP and a surface RFCD provides a pressure seal and a barrier between the external environment and the wellbore returns, such a configuration can be problematic. If the subsurface BOP fails, or if there is a sudden release of gas or pressurized fluid into the riser for any other reason (for example, solution gas assuming gaseous form as it ascends the riser), control of the pressurized gas or fluid in the riser occurs at the level of the drilling platform using the surface BOP stack, the surface RFCD and the diverter. This can result in exposure of the drilling platform to dangerous risk if the pressure and volume of the wellbore return within the riser exceeds the pressure rating of the riser, or if the capacity of the surface equipment to deal with this type of event is not adequate.
These problems may be mitigated by positioning the RFCD in the riser below the slip joint, which is typically the weakest pressure rated assembly in the riser string. In this manner, the RFCD creates a pressure seal that isolates the pressurized wellbore returns in the riser below the drilling platform so that they can be contained and diverted if required at a subsurface level thereby substantially eliminating the exposure of the drilling platform to danger, and giving the riser greater than typical pressure integrity.
U.S. 2006/0102387 to Bourgoyne et al, describes a RFCD releasably positioned in a riser by a holding member that is threaded to the RFCD. In use, the assembled holding member and RFCD are run down the riser together, until their movement is resisted either by lugs on the holding member that engage an internal shoulder of the riser, or a passive latching mechanism between the holding member and an internal formation of the riser. The holding member adds weight to the drill string, and a retractable seal is required between the holding member and the interior of the riser to permit passage of the holding member.
WO 2013006963 to Boyd et al, describes a RFCD integrated into the riser by a stationary housing having a flanged connector that is, in use, sandwiched between the flanges of two adjacent riser pipe sections. However, the flange connection of the stationary housing must be made complementary to the flanges of the adjacent riser pipe sections.
Accordingly, there is a need for a system to secure a RFCD in a riser to create an additional pressure seal between the wellbore and the external environment, which provide an alternative to the prior art, which may mitigate some of the difficulties of the prior art.